Lance Armstrong admitted cheating in each of his seven Tour de France wins

Cycling's showpiece event the Tour de France, which started last weekend, has been marred with controversy for years.

Latterly, after years of fiercely denying allegations, former US cyclist Lance Armstrong admitted in 2013 that he used performance-enhancing drugs to win each of his seven Tour de France titles.

His former rival Alberto Contador, who is competing in this year's edition of the race, was handed a two-year ban in 2012 and stripped of his 2010 Tour de France victory. Contador has always maintained his innocence, and blamed the failed drug test on eating contaminated meat.

According to David Fraser, MD at PR firm Ready10, years of doping revelations have left the public "tired and suspicious".

He said: "This is a long-standing problem for the sport and despite nearly five years passing since the Lance Armstrong revelations, it still has a huge way to go to recover its reputation."

Drugs and sexism deter sponsors

The sport also faced allegations of sexism last year after former British Cycling technical director Shane Sutton was accused of using inappropriate and discriminatory language toward female cyclist Jess Varnish.

Andy Sutherden, global head of sport and partnership marketing at Hill+Knowlton Strategies, said that because of these issues, cycling has struggled to attract a number of "major" commercial partners.

"There is also a concern that the better you are at cycling, the more obligated you are to prove your innocence," Sutherden said of the drugs issue.

He argued that the sport was "on the road to recovery", but said it still needed "a big personality", its own Usain Bolt, to help speed up the process.

Paddy Hobbs, head of sport at Pretty Green, said the Tour faced "a massive uphill struggle" to shake off its perception as a dirty sport.

Echoing Sutherden's remarks, he said: "At a time where it's also lacking in major credible personalities, the Tour desperately needs a new hero to emerge and become its poster boy to take it into a new, cleaner, era."

Le Tour 'retains an allure'

In contrast, Neil Hopkins, director at M&C Saatchi Sport & Entertainment, said that no matter how entrenched problems with doping seemed, the race "retains an allure for fans, participants and sponsors alike".

He said: "Despite the results of seven Tours being voided between 1999 and 2005 because of Lance Armstrong's admission that his remarkable run of success was drug-induced, sponsors remain loyal to an event that sits at the zenith of one of Europe's most popular sports."

According to figures compiled by social media monitoring tool Brandwatch, of more than 201,000 mentions globally of the Tour on Twitter in the past week, over 71 per cent of the conversation has been positive.

Terms such as "doping" (450), "drugs" (260), and "cheating" (190) have been mentioned fewer than 1,000 times since the race began, Brandwatch said.

The majority of the negative comments focus on Mark Cavendish, who broke his shoulder after being knocked off his bike by fellow rider Peter Sagan.